In recent years, in the field of microfabrication when manufacturing semiconductor elements and liquid-crystal elements, miniaturization has advanced rapidly thanks to the development of lithographic technology. Irradiation using shorter wavelengths is usually employed for such miniaturization. In particular, conventionally used g-line (wavelength: 438 nm) or i-line (wavelength: 365 nm) ultraviolet rays are now being replaced by DUV (deep ultraviolet) light. Currently, lithographic technology using a KrF excimer laser (wavelength: 248 nm) has been introduced to the market, and lithographic technology using ArF excimer laser (wavelength: 193 nm) is being developed for applications using even shorter wavelengths. Moreover, research and development in lithographic technology has been conducted using an F2 excimer laser (wavelength: 157 nm) as a next-generation technology. As for lithographic technologies slightly different from those above, technologies using electron beams or using extreme ultraviolet light (EUV light) with a wavelength around 13.5 nm have been also researched assiduously.
As for high-resolution resist for irradiation light with shorter wavelengths or for electron beams, “chemically amplified resist” containing a photoacid generator has been proposed. Improvement and development of chemically amplified resists are currently being promoted widely.
As polymers to be used for chemically amplified resists, acrylic polymers using (meth)acrylate esters as a monomer are being developed due to their highly transparent characteristics. Also, to provide various functions for resists, monomers used in such polymers have been improved vigorously on a daily basis. In recent years, as for polymerizable monomers capable of providing resists with resistance to dry etching and adhesiveness to substrates, (meth)acrylate esters with a norbornene lactone skeleton have been proposed. Various methods are being proposed for producing such lactone compounds including their intermediates (see patent publications 1 to 3, for example).
Lactone compounds are widely used as materials for functional chemicals such as pharmaceutical and agricultural products. Especially, polymerizable carboxylic acids such as (meth)acrylic acid may be added to lactone compounds with active carbon-carbon double bonds. Resist materials containing such polymer compounds formed with (meth)acrylate esters with a lactone skeleton have excellent properties such as sensitivity, resolution and etching resistance, and are useful for microfabrication by electron beams or by deep ultraviolet rays.
To obtain lactone compounds by reducing an acid anhydride having a carbon-carbon double bond in the molecule so that only the acid anhydride is selectively reduced while leaving the carbon-carbon double bond in the molecule, combinations of a reduction agent and solvent are known as follows:
(1) a combination of sodium borohydride and N,N-dimethylacetamide (patent publication 4);
(2) a combination of sodium borohydride and ethanol (non-patent publication 1); and
(3) a combination of sodium borohydride and a mixed solvent of tetrahydrofuran and alcohols (patent publication 5).
In addition to being used for the above resists, (meth)acrylate esters are used as a curing component of various photocurable resin compositions such as UV-curable or electron beam-curable resins. Applications of such photocurable resin compositions are paints, ink, adhesives or the like used in plastics, paper, wood, inorganic materials and the like. Recently, applications of such photocurable resin compositions have expanded to electronics material fields such as semiconductors and liquid crystals, optoelectronics fields such as optical fibers and optical lenses, and even to medical fields.
Among such applications, polymers formed with (meth)acrylate esters with a norbornene lactone skeleton as a monomer have not been used so far.